Staggered pole switched reluctance motor

ABSTRACT

A switched reluctance machine includes a first element having a plurality of uniform poles and a second element having a first pole and a second pole. The first pole has a wide face and the second pole has a narrow pole face. The first and second elements are disposed for movement relative to each other such that the wide and narrow poles are moveable in spaced relation to the plurality of uniform poles.

This application is a continuation-in-part of copending application Ser.No. 08/545,085 filed on Oct. 19, 1995, now U.S. Pat. No. 5,852,334.

BACKGROUND OF THE INVENTION

This invention relates to electronically commuted switched reluctancemachines and more particularly to continuous rotation motors operated bysources of polyphase electric energy.

Switched reluctance motors are well known in the art. These motors havea stationary member, typically called a stator, and a movable member,typically called a rotor The rotor and stator are oriented such thatthey move relative to each other. A typical stator includes a yokesupporting a plurality of magnetically permeable poles circumferentiallyspaced and having gaps therebetween. A typical rotor includes amagnetically permeable body comprised of laminations of magneticallypermeable steel forming two or more poles circumferentially spaced andhaving gaps therebetween. The rotor is disposed relative to the statorsuch that their respective poles pass closely adjacent, when the rotoris moved relative to the stator, i.e., the poles of the rotor move inspaced relation to the poles of the stator. The motor has phase windingson the poles of the stator but not on the poles of the rotor. Switchedreluctance motors rely on polyphase electronic commutation to excitethese phase windings in proper sequence to cause movement of the rotorrelative to the stator. Specifically, excitation of the phase windingsproduces on the stator a pole pair having a north pole and a south pole.These phase windings create a magnetic flux path that passes through thepolarized pole pairs, the rotor and the yoke of the stator, i.e., amagnetic circuit. In response to flux passing therethrough, the rotormoves to bring a pair of rotor poles into a minimum reluctance positionrelative to the polarized pair of stator poles. This minimum reluctanceposition corresponds to the maximum inductance of the energized phasewinding. A feature common to two phase SR motors is that the rotor istypically configured to optimize rotation in one direction. Advantagesof switched reluctance motors (hereinafter "SR" motors) are that theyare efficient in converting electrical energy into mechanical work, theyare reliable because of their mechanical simplicity and they are capableof significant rotational speeds, i.e., 100,000 RPM. Additionally, SRmotors are inexpensive to produce, they are rugged and robust and do notrequire brushes or slip rings.

A number of common SR motor configurations and electronic commutationcombinations exist to fulfill certain end use requirements. Somepolyphase source and stator/rotor combinations include, withoutlimitation, two phase 8/4 motor; three phase 6/4 motor; four phase 8/6motor and a five phase 10/8 motor. One reason for increasing the numberof stator and rotor poles and for having higher numbers of phases is toincrease the number of electronic phase commutations per revolutionthereby minimizing torque dips or torque ripple between the phases.

Torque in an SR motor is related to changing inductance (dL) ofenergized phase windings as a function of rotor position. Inductance inan SR motor decreases or increases as the poles of the rotor move intoor out-of alignment with the poles associated with the energized statorwindings, i.e., as the rotor-stator system moves into or out-of aminimum reluctance position. Stated differently, torque is produced whenthere is a change in inductance as a function of angular position, i.e.,dL/dθ; positive torque being produced when the inductance of anenergized phase increases and negative torque being produced when theinductance of an energized phase decreases.

A problem with prior art two phase SR motors is that at certain angularpositions of the rotor relative to the stator, the torque experienced bythe rotor is zero or a very small percentage of maximum torque. Thisposition of little or no torque results from the poles of the rotor andthe stator being positioned relative to each other such thatinsufficient flux from an energized stator pole pair passes through apair of rotor poles to cause relative motion therebetween. Attempts atovercoming this problem included modifying the geometries of the rotorpoles such that portions of the rotor pole are in sufficient fluxcommunication with an energized stator pole to impart torque to therotor.

One such geometry includes a stepped gap rotor wherein a first portionof the face of a rotor pole coming into flux communication with theenergizing stator pole forms a gap with the face of the stator polehaving a first gap space. The second portion of the face of the rotorpole coming into flux communication with the face of the stator poleforms a second gap that is narrower than the first gap space; thetransition between the first gap space and the second gap space being astep.

Another geometry includes a snail-cam design wherein the face of therotor pole tapers such that the gap between the rotor and the statorbecomes progressively smaller as the rotor rotates into minimumreluctance position with respect o the stator. For these pole geometriesthe faces of the rotor poles are widened such that the first portion ofthe rotor pole extends towards an adjacent deenergized stator pole whenthe second portion of the rotor pole is in a minimum reluctance positionwith an energized stator pole. These various rotor pole geometrieseliminate positions of zero torque in a two phase motor, however, suchrotor geometries are unable to produce consistent torque throughout therotation of the rotor. This inconsistent torque, or torque ripple,produced by prior art two phase SR motors is unacceptable for certainapplications, such as washing machines, fluid pumps, traction motors,position servos and the like, wherein significant torque may be requiredat any position of the rotor relative to the stator.

An attempt at overcoming torque ripple in SR motors includes increasingthe number of commutation phases to 3 or more. It is well known thattorque ripple generally decreases with an increasing number of motorphases. Specifically, 3 phase motors generally have less torque ripplethan 2 phase motors, 4 phase motors have less torque ripple than 3 phasemotors and so on. The decrease in torque ripple with increasing phasesresults from the dL/dθ from one phase being non-zero before the dL/dθfrom an immediately preceding phase becoming zero. Thus, increasing thenumber of phases to 3 or more produces closely adjoining or overlappingdL/dθ such that the rotor experiences torque from the energization ofone phase before the termination of torque from the energization ofanother phase. This continuity of torque or overlap in torque betweenphases of an SR motor results in a more continuous torque having lesstorque ripple. Problems with SR motors having 3 or more phases, however,are the increased quantity of components for the commutationelectronics, and consequently the cost thereof; the increased number ofconnections between the commutation electronics and the phase windings;the increased resolution of position sensors required to resolve theposition of the rotor for the electronic commutation; and more acousticnoise over 2 phase SR motors.

It is the object of the present invention to provide a new and improvedSR motor that overcomes the above-referenced problems and others.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a switchedreluctance motor having an inner stator with a plurality of evenlyspaced, outwardly extending poles disposed thereon. An annular rotorsurrounds the stator and is mounted for rotation about a longitudinalaxis relative to the poles of the stator. The rotor has a plurality ofinward extending poles disposed thereon. At least one of the rotor poleshas a rotor pole face of a first size and another of the rotor poles hasa rotor pole face of a second size greater than the first size. Windingsfor two phases are wound about poles of the stator that are separated bya winding and an associated stator pole of the opposite phase. A phasewinding is disposed around a pole of the stator and electricallyconnected to one phase of an electrical power source for energizationthereby.

In accordance with another aspect of the present invention, there isprovided an SR motor having a stator with a plurality of magneticallypermeable stator poles evenly spaced circumferentially about a centralaxis, each of the stator poles extending outward from the axis andtraversing a first stator angle. An annular rotor is mounted forrotation relative to the stator about the axis. The rotor has an evennumber of magnetically permeable poles unevenly spaced about the axis.The rotor poles extend toward the axis and include a pole having anarrow face that traverses a first rotor angle, wherein the first rotorangle is approximately equal to the first stator angle, and a polehaving a wide face that traverses a second rotor angle that isapproximately twice the first rotor angle.

In accordance with another aspect of the present invention, there isprovided a switched reluctance motor driven by a two phase source havinga stator having a plurality of evenly spaced like poles defining auniform gap between adjacent stator poles. Windings for each of the twophases of the motor are wound about stator poles that arecircumferentially separated by a winding and an associated stator poleof a different phase. A rotor is mounted for rotation around the statorand has a wide rotor pole and a narrow rotor pole. The rotor isdimensioned such that a first sector of the wide rotor pole is inalignment with a first stator pole when the narrow rotor pole is alignedwith a second stator pole and a second sector of the wide rotor pole isin alignment with the first stator pole when the narrow rotor pole isaligned with the gap adjacent the second stator pole.

In accordance with another aspect of the present invention, there isprovided a switched reluctance motor driven by a two phase source havinga stator with a plurality of like poles, each having a stator pole face.The stator poles are uniformly spaced to define a uniform gap betweenadjacent stator poles. Windings are provided for each of the phases ofthe motor and are wound about stator poles that are circumferentiallyseparated by at least one winding and an associated stator pole of adifferent phase. A rotor is mounted for rotation about the periphery ofthe stator. The rotor has a wide rotor pole face. The rotor isdimensioned such that the narrow pole face is approximately equal to astator pole face and the wide rotor pole face spans at least the poleface of a first stator pole and the gap adjacent the first stator whenthe narrow pole face is aligned with the pole face of a second statorpole.

In accordance with another aspect of the present invention, there isprovided a switched reluctance motor having an inner stator with aplurality of evenly spaced like stator poles, the number of stator polesbeing a whole multiple of four. A rotor having a plurality of rotorpoles is mounted for rotation around the stator. The number of rotorpoles is one-half the number of stator poles, and half of the rotorpoles are wide rotor poles and half of the rotor poles being narrowrotor poles. A narrow rotor pole is disposed on each side of a widerotor pole. The rotor dimensioned such that the narrow rotor poles havepole has a pole face approximately equal to the pole face of a statorpole and the gap between adjacent stator poles. Windings for two phasesare wound about stator poles that are circumferentially separated by atleast one winding and an associated stator pole of a different phase. Apair of adjacent stator poles is connected to have the same polarity.

In accordance with another aspect of the present invention, there isprovided a switched reluctance motor driven by a two phase source havingan inner stator with a plurality of evenly spaced like poles defining auniform gap between adjacent stator poles. Windings for each of the twophases of the motor are wound about stator poles that arecircumferentially separeted by a winding and an associated stator poleof a different phase. A rotor is mounted for rotation around the statorhaving a wide rotor pole and a narrow rotor pole. The rotor isdimensioned such that the energization of a phase causes a wide rotorpole to interact with a first stator pole to induce a first torque onthe rotor and to produce a first predetermined angular rotation of therotor, and thereafter a first narrow pole interacts with a second statorpole to induce a second torque on the rotor and to produce a secondpredetermined angular rotation on the rotor.

In accordance with another aspect of the present invention, there isprovided a switched reluctance motor driven by a two phase source havingan inner stator with a plurality of evenly distributed, like polesthereon, each of the poles having a stator pole face. Windings for eachof the phases of the motor are wound about stator poles that arecircumferentially separated by at least one winding and an associatedstator pole of a different phase. An outer rotor mounted for rotationaround the stator. The rotor has a wide rotor pole having a wide rotorpole face and a narrow rotor pole has a narrow rotor pole face. Therotor is dimensioned such that energization of one of the phases causesa predetermined angular rotation of the rotor wherein a first portion ofthe angular rotation is created by a wide rotor pole being drawn into aminimum reluctance position relative to one of the energized statorpoles and the other portion of the angular rotation is created by anarrow rotor pole being drawn into a minimum reluctance position withanother of the energized stator poles.

In accordance with another aspect of the present invention, there isprovided a switched reluctance motor driven by a two phase source havinga stator with a plurality of like poles evenly distributed thereon todefine a uniform gap between each pole, each of the poles having astator pole face. Windings for each of the phases of the motor are woundabout stator poles that are circumferentially separated by at least onewinding and an associated stator pole of a different phase. An annularrotor is mounted for rotation around the stator. The rotor has a widerotor pole having a wide rotor pole face and a narrow rotor pole havinga narrow rotor pole face. The rotor is dimensioned such that a uniformgap is defined between the rotor pole faces and the stator pole facesand energization of one of the phases, wherein the wide rotor polemagnetically interacts with a first stator pole and the narrow rotorpole magnetically interacts with a second stator pole to cause the rotorto rotate a predetermined angular amount wherein the area of overlap ofthe wide rotor pole face and the narrow rotor pole face relative to thefirst and second stator poles faces increase at a generally uniform rateas the rotor moves the predetermined angular amount.

In accordance with another aspect of the present invention, there isprovided a switched reluctance motor driven by a two phase source. Themotor has an inner stator having a plurality of like poles evenlydistributed thereon, each of the poles having a stator pole face.Windings for each of the phases of the motor are wound about statorpoles that are circumferentially separated by at least one winding andan associated stator pole of a different phase. A rotor surrounds thestator and is mounted for rotation relative to the stator. The rotor hasa wide rotor pole having a wide rotor pole face and a narrow rotor polehaving a narrow rotor pole face. The rotor poles are dimensionedrelative to the stator poles such that the motor has aninductance-to-angular rotation profile, wherein the inductance of aphase increases over a first angle of rotation and decreases over asecond angle of rotation and the first angle of rotation isapproximately twice the second angle of rotation.

In accordance with another aspect of the present invention, there isprovided a switched reluctance motor driven by a two phase sourcecomprising: a stator having a yoke and a (2 X) number of evenly spaced,like poles distributed on the yoke defining a gap between each statorpole. Windings for each of the two phases of the motor are wound aboutstator poles that are circumferentially separated by a winding and anassociated stator pole of a different phase. A rotor is mounted forrotation relative to the stator. The rotor having (X) number of rotorpoles and the rotor is dimensioned such that, during each phaseenergization, the motor has a first state wherein (1/2 X) number ofrotor poles are magnetically coupled to a like number of stator polesand a second state wherein (X) number of rotor poles are magneticallycoupled to a like number of stator poles.

In accordance with another aspect of the present invention, there isprovided a switched reluctance motor driven by a two phase source,comprising a stator having a yoke and an even number of evenly-spaced,like stator poles distributed on the yoke defining a gap between eachstator pole. Windings for each of the two phases of the motor are woundabout stator poles that are circumferentially separated by a winding andan associated stator pole of a different phase. A rotor is mounted forrotation relative to the stator. The rotor has an even number of rotorpoles, and the rotor poles are dimensioned such that when the phases arealternately energized, the rotor poles operatively interact with thestator poles such that the motor oscillates between a first statewherein half of the rotor poles are magnetically coupled to a likenumber of the stator poles, and a second state wherein all of the rotorpoles are magnetically coupled to a like number of stator poles.

An advantage of the present invention is the improved torque experiencedby the rotor at all positions of the rotor relative to the stator.

Another advantage of the present invention is the improved torquecharacteristics of a 2 phase SR motor making a two phase SR motorapplicable to applications heretofore requiring an SR motor having 3 ormore phases.

Still another advantage of the present invention is reduced torqueripple.

Yet another advantage of the present invention is the improvedelectrical power output over prior art generators.

A still further advantage of the present invention is a two phase, SRmotor having an inner stator and an outer rotor.

A still further advantage of the present invention is a two phase SRmotor that is quieter than two-phase SR motors known heretofore.

A still further advantage of the present invention is a two phase SRmotor that, during each phase energization, has a first state wherein apredetermined number of rotor and stator poles are magnetically coupled,and a second state wherein twice said predetermined number of rotor andstator poles are magnetically coupled.

Still further advantages of the present invention will become apparentto those of ordinary skill in the art upon reading and understanding thefollowing detailed description of the preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an 8/4 switched reluctance motor inaccordance with the present invention.

FIG. 2 is the motor of FIG. 1 with associated control and operationalcircuitry connected thereto and showing the rotor advanced by 15mechanical degrees relative to the motor of FIG. 1.

FIGS. 3-4 are isolated views of the rotor and stator of FIG. 1 showingthe rotor advanced by 30 and 45 mechanical degrees respectively relativeto the motor of FIG. 1.

FIGS. 5(a)-5(f) are isolated views of the rotor and stator of FIG. 1showing mechanical progression of the rotor in a CCW direction relativeto the stator in response to the generation of north and south polepairs by the excitation of the phase A and phase B windings, removed forthe purpose of illustration.

FIGS. 6(a)-6(f) are flux plots corresponding to the phase energizationand rotor and stator positions of FIGS. 5(a)-5(f).

FIG. 7(a) is an exemplary ideal inductance profile of the phase A andphase B stator windings of FIG. 1 with respect to the CCW mechanicalprogression of the rotor relative to the stator.

FIG. 7(b) is an ideal energization profile of the phase A and phase Bwindings of FIG. 1 for the inductance profile of FIG. 7(a).

FIG. 8 is an inductance profile of the phase A and phase B statorwindings of FIG. 1 with respect to the CCW progression of the rotorrelative to the stator.

FIG. 9(a) is the static torque curves for the Phase A and Phase Bwindings at 1.5A, 2.0A, 2.5A and 3.0A phase energization current for theinductance profile of FIG. 8.

FIG. 9(b) is an energization profile of the phase A and phase B statorwindings for the static torque curves of FIG. 9(a).

FIG. 9(c) is the torque curves resulting from the combination of thePhase A and Phase B torque curves of FIG. 9(a).

FIG. 10 is a sectional view of an 16/8 switched reluctance motor inaccordance with the present invention.

FIG. 11(a) is a sectional views of an 4/2 switched reluctance motor inaccordance with the present invention with associated control andoperational circuitry connected thereto.

FIGS. 11(b)-11(c) are isolated views of the 4/2 switched reluctancemotor of FIG. 11(a) showing the rotor advanced by 45 and 90 degreesrespectively relative to the motor of FIG. 11(a) in response to thegeneration of north and south pole pairs by the excitation of the phaseA and phase B windings.

FIG. 12 is a linear actuator in accordance with the present invention.

FIGS. 13(a)-13(e) are isolated views of a rotor and stator in accordancewith a stator implementation of the present invention showing mechanicalprogression of the rotor in a CW direction relative to the stator inresponse to the generation of north and south pole pairs by theexcitation of phase A and phase B windings, removed for illustrationpurposes.

FIG. 14 is a sectional view of a switched reluctance motor-generator inaccordance with the present invention with associated control andoperational circuitry connected thereto.

FIG. 15 is a sectional view of an 8/4, 2-phase switched reluctance motorhaving an inner stator and an outer rotor illustrating an alternateembodiment of the present invention.

FIG. 16 is a sectional view of the motor shown in FIG. 15, showing therotor advanced clockwise 15 mechanical degrees relative to the stator.

FIGS. 17 and 18 are views of the motor shown in FIG. 15, showing therotor advanced clockwise by 22.5 and 45 mechanical degrees,respectively, relative to the stator.

FIG. 19 is an ideal energization profile of phases A and B of the motorshown in FIG. 15.

FIGS. 20-23 are sectional views of the motor shown in FIG. 15, showingflux plots corresponding to the rotor and stator positions shown inFIGS. 15-18.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIG. 1, a sectional view of a two phase 8/4 switchedreluctance motor 10 in accordance with the present invention isillustrated. The motor has a stator 12 having a magnetically permeablemember 14 disposed around a central bore 16 and defining a plurality ofpoles 18(a)-18(h). In the embodiment of FIG. 1 the stator has an evennumber of poles, and while eight poles are shown in FIG. 1, the statorcan have a different even number of poles. A rotor 20 is disposed in thecentral bore for rotation therein. The rotor has 4 poles 22(a)-22(d),however, the rotor can have a different even number of poles. Phasewindings 24, 26 are disposed around the phase A and phase B stator polesrespectively for generating magnetic fields that extend from the statorpoles into the central bore. Phase windings 24 and 26 are alternatelydisposed on every other stator pole and are wound such that for everypole of one polarity there is a corresponding pole of an oppositepolarity. In the illustrated embodiment, phase A poles 18(a) and 18(c)are north poles and phase A poles 18(e) and 18(g) are south poles.Similarly, phase B poles 18(f) and 18(h) are north poles and phase Bpoles 18(b) and 18(d) are south poles. It is to be appreciated, that thepole polarity is for illustration purposes only and is not to beconstrued as limiting the invention.

With reference to FIG. 2 and continuing reference to FIG. 1, phasewindings A and B are series connected to sources of switched current 30and 32 respectively such that current flows through the phase windingsonly in one direction. It is to be appreciated, however, that the phasewindings could be parallel connected or combination series-parallelconnected to their respective sources of switched current. A positionsensor 36, such as a hall effect sensor, a resolver or an encoder, isconnected between the rotor and the stator for determining the positionof the rotor relative to the stator. Alternatively, self inductance ofthe phase windings are used to determine the position of the statorrelative to the rotor. The position sensor has an output connected to acontroller 38 for reporting the angular position of the rotor relativeto the stator. The controller 38 is connected to the phase A and phase Bphase drivers for controlling the firing of the respective phases inaccordance with the position of the rotor relative to the stator. Anoptional speed control 39 connected to controller 38 provides foradjustment of the rotational speed of the rotor. In the FIG. 2embodiment, motor 10 is a unidirectional motor in which the rotorrotates counterclockwise (CCW) with respect to the stator. It is to beappreciated, however, that motor could be designed for clockwise (CW)rotation and that the direction of rotation is not to be construed aslimiting the invention.

With reference to FIG. 3, the poles of the rotor are disposed unevenlyabout the circumference thereof. With reference to a longitudinal axis40 of the rotor, the angle between rotor poles 22(a)-22(b) and22(c)-22(d) is a first angle 41, and the angle between rotor poles22(b)-22(c) and 22(a)-22(d) is a second angle 42, greater than the firstangle. Moreover, as shown in FIG. 4, the faces of the wide rotor polesspan a third angle 43 and the faces of the narrow rotor poles span aforth angle 44 less; the third angle being greater than the forth angle.In the preferred embodiment, at the circumference of the rotor, the faceof the wide rotor poles are twice as wide as the face of the narrowrotor poles. At the inside circumference of the stator the face of thestator poles are approximately the same width as the face of the narrowrotor poles and the distance between adjacent stator poles isapproximately the width of a stator pole.

With reference to FIGS. 5(a)-5(f), the CCW progression of the rotor withrespect to the stator, in response to the generation of north-south polepairs by the excitation of associated phase windings, is illustrated. InFIGS. 5(a)-5(f) the phase windings, the phase A and phase B drivers, thecontroller/power supply, the speed control and the position sensor ofFIGS. 1 and 2 have been omitted to facilitate uncluttered views of therotor and stator. To facilitate an understanding of when the omittedphase windings of FIGS. 5(a)-5(f) are energized, the poles associatedwith an excited phase are marked with either an `N` or an `S` to signifya north or south pole respectively. In operation, starting from the zerodegree CCW rotor position of FIG. 5(a), the controller 38 causes thephase B current source 32 to energize the phase B windings in theabsence of excitation of the phase A windings. This excitation producesa CCW torque on the rotor causing the rotor to align the wide rotorpoles with excited phase B stator poles 18(d) and 18(h), i.e., the rotorpoles move into minimum reluctance position with respect to the phase Bpoles--the minimum reluctance position corresponding to the maximuminductance of the energized phase windings producing said alignment. InFIG. 5(b), at 22.5 degrees CCW rotor position, the wide rotor poles andadjacent energized phase B stator poles are in a minimum reluctanceposition with respect to each other as a result of a constant gap beingformed therebetween. However, the inductance of the phase B windingsincreases due to the narrow rotor poles 22(b) and 22(d) moving to aminimum reluctance position with stator poles 18(b) and 18(f).Accordingly, the rotor experiences a torque due to the interaction ofthe narrow rotor poles with the energized phase B windings whileexperiencing little or no torque from the interaction of the wide rotorpoles with the energized phase B windings. In this manner, torqueexperienced by the rotor shifts from the wide rotor poles to the narrowrotor poles. In FIG. 5(c), at 30 degrees CCW rotor position, the rotorexperiences CCW torque from the energized phase B windings incooperation with the increasing inductance thereof caused by the narrowrotor poles moving to a minimum reluctance position with phase B statorpoles 18(b) and 18(f). It is to be appreciated that between 22.5 and 45degrees rotor position the gap, and therefore the reluctance, betweenthe wide rotor poles and stator poles 18(d) and 18(h) is substantiallyconstant and therefore the rotor experiences no torque from interactionof the energized phase B windings and wide rotor poles. In FIG. 5(d), at45 degrees CCW rotor position, the wide and narrow rotor poles are inminimum reluctance position with energized phase B stator poles18(d)-18(h) and 18(b)-18(f) respectively. Accordingly, at this positionno torque is imparted to the rotor from the energization of the phase Bwindings. Energizing the phase A windings at 45 degrees CCW rotorposition, however, causes flux to flow from phase A poles 18(a) and18(e) through the wide rotor poles. In response to flux flowingtherethrough, the rotor experiences a CCW torque causing the rotor toalign the wide poles with the poles of the excited phase A windings. Asthe rotor moves past 45 degrees CCW rotor position, however, theenergized phase B windings experience a decrease in inductance due tothe increasing reluctance between the stator poles of the phase Bwindings and the rotor poles. To avoid having the rotor experience a CW(negative) torque from energization of the phase B windings incooperation with the decreasing inductance thereof, the phase B windingsare deenergized. In this manner, the torque experienced by the rotorshifts from the phase B windings to the phase A windings. In FIG. 5(e),at 67.5 degrees of CCW rotor rotation, the wide rotor poles andenergized phase A stator poles 18(a) and 18(e) are in a minimumreluctance position such that no torque is imparted to the rotor fromthe interaction thereof. The inductance of the energized phase Awindings, however, is increasing due to the narrow rotor poles cominginto flux communication with energized phase A stator poles 18(c) and18(g). Thus, torque imparted to the rotor from the energized phasewindings shifts from the wide rotor poles to the narrow rotor poles. InFIG. 5(f), at 90 degrees of CCW rotor rotation, the wide and narrowrotor poles are in minimum reluctance alignment with stator poles18(a)-18(e) and 18(c)-18(g) respectively. Accordingly, the rotorexperiences no torque from the interaction of the wide rotor poles withthe phase A windings. Energizing the phase B windings, however, causesflux to flow from phase B poles 18(b) and 18(f) through the wide rotorpoles. In response to the energization of the phase B windings, therotor experiences a CCW torque causing the rotor to align the wide poleswith the excited phase B windings. To avoid having the rotor experiencea CW (negative) torque from energization of the phase A windings incooperation with the decreasing inductance thereof, the phase A windingsare deenergized.

With reference to FIGS. 6(a)-6(f), magnetic flux plots corresponding tothe rotor positions and phase energizations of FIGS. 5(a)-5(f) areillustrated. In FIGS. 6(a)-6(b), between 0 and 22.5 degrees CCW rotorposition a greater amount of flux flows through the wide rotor polesthan through the narrow rotor poles. Referring to FIGS. 6(b)-6(c),between 22.5 and 30 degrees CCW rotor position the amount of fluxpassing through the narrow rotor poles increases as the narrow rotorpoles move into minimum reluctance position with stator poles 18(b) and18(f). With reference to FIG. 6(d), at 45 degrees rotor position, thephase B windings are deenergized and the phase A windings are energizedsuch that flux flowing through the rotor shifts from the phase Bwindings to the phase A windings. With reference to FIGS. 6(d)-6(e),flux produced by the energization of the phase A windings between 45 and67.5 degrees rotor position initially passes through the wide rotorpoles and increases through the narrow rotor poles as the narrow polesmove into minimum reluctance position with stator poles 18(c) and 18(g).With reference to FIG. 6(f), at 90 degrees rotor position, the phase Awindings are deenergized and the phase B windings are energized.

In the foregoing description the rotor is advanced through 90 mechanicaldegrees by the selective energization and deenergization of the phase Aand phase B windings in relation to the position of the rotor relativeto the stator. It is to be appreciated, however, that the abovedescription is extendable to movement of the rotor beyond 90 mechanicaldegrees. Moreover, it is to be appreciated that the increasing ordecreasing inductance of a phase winding corresponds to the respectivedecreasing or increasing reluctance in the magnetic flux path associatedwith said phase winding.

The present invention produces in the phase A and phase B windings achange in inductance with angular position (dL/dθ) having a slope thatincreases at a first rate and decreases at a second rate. Specifically,with reference to FIGS. 7(a)-7(b), and continuing reference to FIGS.5(a)-5(f), an exemplary ideal inductance profile for the change ininductance of the phase B windings 50 and the phase A windings 52 as afunction of the CCW position of the rotor and in relation to idealenergization of the phase A and phase B windings is illustrated. It isto be appreciated that the FIGS. 7(a)-7(b), are for illustrationpurposes and are not to be construed as limiting the invention. At 0degree rotor position, the phase B windings are energized in the absenceof the energization of the phase A windings. In response, the rotorexperiences a CCW torque that urges the rotor and stator combinationtowards a minimum reluctance, maximum inductance, position. Concurrentwith the increasing inductance of the phase B windings the inductance ofphase A windings is decreasing. As illustrated in FIG. 7(a), theinductance of each phase of the novel pole configuration decreases morerapidly than it increases. This allows for advantageous overlap of theincreasing inductance of the phase A and phase B windings. Specifically,at 37 degrees rotor position, the inductance of phase A windingstransitions from decreasing to increasing and the phase A windings areenergized. Between 37 degrees and 45 degrees rotor position, both phasewindings are energized and the inductance of both phase windings areincreasing. Accordingly, the rotor experiences torque from both thephase A and phase B windings. At 45 degrees rotation, and with the phaseA windings energized, the phase B inductance transitions from increasingto decreasing and the phase B windings are deenergized. In this manner,the rotor experiences a positive CCW torque from the energization of thephase A windings in cooperation with the increase in inductance thereofwhile avoiding a negative CW torque from the energization of the phase Bwindings in cooperation with the decrease in inductance thereof. At 82degrees of rotation, the inductance of the phase B windings transitionsfrom decreasing to increasing and the phase B windings are energized.Between 82 and 90 degrees of rotation the increasing inductance of thephase A and phase B windings in cooperation with the energizationthereof imparts a torque to the rotor. At 90 degrees of rotation, theinductance of the phase A windings transitions from increasing todecreasing and the phase A windings are deenergized such that torque isimparted onto the rotor exclusively from the increasing inductance ofphase B in cooperation with the energization thereof. At 127 degreesrotation, the inductance of phase A transitions from decreasing toincreasing and the phase A windings are energized. Accordingly, between127 and 135 degrees rotor position the phase A and phase B windingsimpart a torque to the rotor. At 135 degrees rotation, the inductance ofthe phase B windings transitions from increasing to decreasing and thephase B windings are deenergized such that the torque imparted onto therotor is exclusively from the increasing inductance of phase A incooperation with the energization thereof.

From the foregoing, it should be appreciated that the present inventionproduces in the phase A and phase B windings a change in inductance as afunction of rotor position wherein the inductance of a phase windingincreases at a different rate than the inductance thereof decreases.Specifically, the increasing inductance of each phase extends over agreater angular position than the decreasing inductance thereof. By wayof example and not of limitation, with reference to FIG. 7(a), the phaseB inductance decreases between 45 and 82 degrees rotor position, i.e.,over 37 mechanical degrees, and increases between 82 and 135 degreesrotor position, i.e., over 53 mechanical degrees. Similarly, the phase Ainductance increases between 37 and 90 degrees rotation, i.e., over 53mechanical degrees, and decreases between 90 and 127 degrees rotation,i.e., over 37 mechanical degrees. The differing slopes of increasing anddecreasing inductance of the phase A and phase B windings allows for theadvantageous overlap thereof as illustrated in FIG. 7(a) and describedabove. This overlap of increasing inductance in cooperation with theselective energization of the phase A and phase B windings provides fortorque to be imparted onto the rotor at all positions of the rotorrelative to the stator.

With reference to FIG. 8, and continuing reference to FIGS. 7(a)-7(b),an inductance profile of the embodiment illustrated in FIGS. 5(a)-5(f)is illustrated. In contrast to the ideal inductance profile of FIGS.7(a)-7(b), the inductance profile of FIG. 8 illustrates that thetransition between increasing and decreasing inductance of the phase Aand phase B windings occurs gradually as the rotor poles move into andout-of alignment with the stator poles. Because positive, CCW, torque onthe rotor is a function of increasing inductance of an energized phasewinding, it is desirable to coordinate the energization of the phasewindings with the rotor position to ensure the phase windings areexperiencing an increasing inductance when energized. Thus, by way ofexample and not of limitation, with reference to FIG. 8, at 0 degreesrotor position the phase B windings are energized and the phase Awindings are deenergized. Between 40 and 44 degrees rotor position thephase A windings are energized and the phase B windings are deenergizedin a manner that results in minimal torque ripple being experienced bythe rotor as the torque imparted to the rotor transitions from the phaseB windings to the phase A windings. Similarly, between 85 and 89 degreesof rotor position, the phase A windings are deenergized and the phase Bwindings are energized in a manner that results in minimal torque ripplebeing experienced by the rotor. It is to be appreciated, however, thatthe inductance of the respective phases instantaneous energization anddeenergization thereof. Accordingly, in practice, the energization anddeenergization of the respective phases is timed to occur such that thetorque experienced by the rotor is optimized. Thus, by way of examplyand not by way of limitation, at approximately 40 degrees of rotorrotation the phase B windings are deenergized such that the energystored therein is dissipated in advance of the phase B windingsexperiencing a decreasing inductance thereby imparting a negative CWtorque onto the rotor. Similarly, at approximately 40 degrees of rotorrotation the phase A windings are energized thereby imparting a positiveCCW torque onto the rotor. Because of the advantageous overlap ofincreasing inductance of the phase A and phase B windings, theenergization for the respective windings can be timed to optimize thetorque experienced by the rotor. Under ideal conditions the rotorexperiences a relatively constant torque with rotor position. Inpractice, however, the rotor experiences some torque dip as the torqueimparted thereon transitions between the respective phase windings.

It is believed that the width of the rotor poles affect the inductanceprofile of FIG. 8. Specifically, with reference to FIG. 4, the face ofthe narrow poles, 22(b) and 22(d) are approximately the same width asthe face of the stator poles while the face of the wide rotor poles,22(a) and 22(c), are illustrated as being approximately the same widthas the combined width of the face of a stator pole and an adjacentspace, e.g., stator pole 22(a) and space 52. This arrangementadvantageously provides for the aforementioned overlap of increasinginductance of the phase windings. It is believed, however, that theoverlap of the phase A and phase B inductance profiles are adjustable bymodifying the width of rotor poles. For examply, narrowing the wide andnarrow rotor poles results in an inductance profile wherein there islittle or no overlap of increasing inductance as the torque on the rotortransitions between the wide rotor poles and the narrow rotor poles.Similarly, widening the wide and narrow rotor poles increases theoverlap of the increasing inductance of the respective phase A and phaseB windings. It is believed, however, that the widening or narrowing ofthe width of the rotor poles excessively will result in undesirabletorque dips. Moreover, widening one of the wide or narrow rotor polesand narrowing the other rotor poles will result in variations in theoverlap of increasing inductance. In like manner, it is also believedthat modifying the width of the stator poles also affects the overlap ofthe phase A and phase B inductance profiles.

With reference to FIGS. 9(a)-9(b), torque curves for the embodimentshown in FIGS. 5(a)-5(f), at different phase winding energizationcurrents, i.e., 1.5A, 2.0A, 2.5A and 3.0A, are illustrated in relationto the phase energization profile thereof. These torque curvesillustrate the torque imparted to the rotor from the energization of therespective phase windings and the advantageous overlap thereof. It is tobe appreciated that the torque experienced by the rotor is the sum ofthe torque produced by the energization of the respective phase A andphase B windings. Thus, as shown in FIG. 9(c), when phases A and B areboth energized, e.g., between 40 and 45 degrees rotor position, thetorque experienced by the rotor is the sum of the torque imparted to therotor from the energization of the respective phase A and phase Bwindings. The FIG. 9(a) torque curves illustrate that the narrow rotorpoles coming into flux communication with the energized phase windingsproduce greater torque ripple at higher phase energization currents,e.g., 2.5A and 3.0A, and lower torque ripple at lower phase energizationcurrents, e.g., 2.0A and 1.5A. Specifically, with reference to the 3.0Atorque curve of FIG. 9(a), between 15 and 22.5 degrees rotor position,the increasing inductance of the energized phase B windings, from thewide rotor poles moving into a minimum reluctance position with thestator poles, imparts a torque onto the rotor. Around 19 degrees rotorposition, however, the wide and narrow rotor poles interact with theenergized phase B windings to produce a torque dip. It is believed thatthis torque dip results from the magnetic saturation of the edge of thenarrow poles first coming into flux communication with the energizedphase windings. As the narrow rotor poles advance into greater fluxcommunication with the energized phase windings, the distribution of themagnetic flux therethrough increases thereby avoiding localized magneticsaturation of the narrow rotor pole. This increased distribution ofmagnetic flux in the narrow rotor pole in turn results in the rotorexperiencing an increase in torque as the rotor advances to 22.5 degreesrotor position. Similar comments apply in respect of the torque on therotor from the cooperation of the increasing inductance of the excitedphase A windings at 64 and 154 degrees rotor position and the excitedphase B windings at 109 degrees rotor position. It should be noted inFIG. 9(a) that torque dip decreases with decreasing phase energizationcurrent.

The energization of the phase A and phase B windings are selected tocoincide with the position of the rotor relative to the stator. In FIG.9(b), the energization of the phase A and phase B windings areillustrated as overlapping to take advantage of the increasinginductance of the respective phase A and phase B windings as a functionof rotor position. In this manner, the rotor experiences minimal torqueripple with rotor rotation. It is to be appreciated, however, that thetorque curves and energization profiles of FIGS. 9(a)-9(b) are forillustration purposes and should not to be construed as limiting theinvention. Specifically, the overlap of the energization of the phase Aand phase B windings could be more or less, or the energization of thephase A and phase B windings could have no overlap depending on, withoutlimitation, the inductance of the windings, the capacity of thecommutation electronics to quickly deenergize the phase windings, therotational speed of the rotor and/or the desired operatingcharacteristics of the motor.

The above embodiments have been described with respect to a two phase8/4 SR motor, however, it is to be appreciated by one skilled in the artthat the 8/4 embodiment set forth above is extendable to embodiments oftwo phase SR motors having different numbers of rotor and stator poles.One such embodiment includes the 16/8 SR motor illustrated in FIG. 10wherein the motor includes phase A and phase B windings disposed aroundalternating stator poles and connected to phase A and phase B phasedrivers, a controller/power supply, and an optional position sensor. InFIG. 10 the polarity of the phase A and phase B poles is not to beconstrued as limiting the invention or as an indication that the phasewindings are energized.

With reference to FIGS. 11(a)-11(c), a 4/2 SR motor embodiment inaccordance with the present invention is illustrated. The motor has astator 60 comprised of a plurality of inwardly extending poles62(a)-62(d) defining a central bore 64. A rotor 66, comprised of twooutwardly extending poles 68(a)-68(b), is disposed in the central borefor rotation therein. Phase windings 70 and 72 are disposed aroundopposing stator poles 62(b)-62(d) and opposing stator poles 62(a)-62(c)respectively for generating magnetic fields that extend from the statorpoles into the central bore. The phase windings 70 and 72 are connectedto the phase A phase driver 30 and the phase B phase driver 32respectively such that current flows through the phase windings in onedirection. A position sensor 36 is connected between the rotor andstator for determining the position of the rotor relative to the stator.The position sensor has an output connected to controller 38 forreporting the angular position of the rotor relative to the stator. Thecontroller 38 is connected to the phase A and phase B phase drivers forcontrolling the firing of the respective phases in accordance with theposition of the rotor relative to the stator. In FIGS. 11(b)-11(c), thephase windings, the phase drivers, the controller/power supply, theposition sensor and the optional speed control of FIG. 11(a) are omittedto facilitate uncluttered views of the rotor and stator. To facilitatean understanding of when the omitted phase windings of FIGS. 11(b)-11(c)are energized, however, the stator poles associated with an excitedphase are marked with an `N` or an `S` to signify a north or south polerespectively.

In operation, starting from the zero degree CCW rotor position of FIG.11(a), the controller 38 causes the phase B phase driver 32 to energizethe phase B windings 72 in the absence of energization of the phase Awindings. The energization of the phase B windings produces a flux thattraverses, without limitation, path 74 passing through energized phase BNorth pole 62(c), wide rotor pole 68(a), deenergized phase A stator pole62(b), and the back iron, or yoke, 76 extending between stator poles62(b) and 62(c). In response tot he flux traversing path 76, the rotorexperiences a CCW torque causing the rotor to align the wide rotor polewith the energized phase B North pole 62(c). Advancement of the rotor tothe 45 CCW degree position of FIG. 11(b), causes the flux to traverse,without limitation, path 78 passing through phase B North pole 62(c),rotor poles 68(a)-68(b), phase B South pole 62(a), and the back iron, oryoke, 76 between phase B poles 62(a) and 62(c). At 45 degrees CCW rotorposition, the wide rotor pole and the energized phase B North pole 62(c)are in a minimum reluctance position with respect to each other becauseof the relatively constant gap 80 formed therebetween. The inductance ofthe phase B winding is increasing, however, due to the narrow rotor pole68(b) moving to a minimum reluctance position with phase B South pole62(a). Accordingly, the rotor experiences a CCW torque from theinteraction of the energized phase B windings and the narrow rotor polewhile experiencing little or no torque from the interaction of the widerotor pole with the energized phase B windings. In this manner torqueexperience by the rotor shifts from the wide rotor pole to the narrowrotor pole. In FIG. 11(c), at 90 degrees CCW rotor position, the wideand narrow rotor poles are in minimum reluctance position with poles62(c) and 62(a) of the energized phase B windings. Accordingly, at thisposition no torque is imparted to the rotor from the energization of thephase B windings. Energizing the phase A windings associated with poles62(b) and 62(d), however, causes flux to traverse, without limitation,path 82 passing through energized phase A South pole 62(d), wide rotorpole 68(a), phase B stator pole 62(c), and the back iron, or yoke, 76extending between stator poles 62(c) and 62(d). In response to the fluxtraversing path 82, the rotor experiences a CCW torque causing the rotorto align the wide rotor pole with the energized phase A South pole62(d). To avoid having the rotor experience a CW (negative) torque, fromthe energization of the phase B windings in cooperation with thedecreasing inductance thereof, the phase B windings are deenergized. Inthis manner torque experienced by the rotor shifts from the phase Bwindings to the phase A windings.

In the foregoing description of a 4/2 SR motor, the rotor is advancedthrough 90 mechanical degrees by the selective energization anddeenergization of the phase A and phase B windings in relation to theposition of the rotor relative of the stator. It is to be appreciated,however, that the above description is extendable to movement of therotor beyond 90 mechanical degrees. Moreover, it is also to beappreciated that, because the rotor of FIGS. 11(a)-11(c) is non-uniformaround the desired center of rotation 40, it is necessary to add weightto the narrow rotor pole or remove material from the wide rotor pole tohave the actual center of rotation coincide with the desired center ofrotation.

With reference to FIG. 12, a unidirectional linear actuator 84 inaccordance with the present invention is illustrated. It is to beunderstood that the linear actuator of FIG. 12 includes phase A andphase B windings disposed around stationary poles 86, 88 and connectedto phase A and phase B phase drivers and a controller/power supply. Likethe embodiment illustrated in FIG. 2, however, the phase windings, thephase drivers and the controller/power supply of FIG. 12 have beenomitted to facilitate an uncluttered view of the linear actuator. Theactuator includes a plunger 90 disposed for linear movement betweenstationary poles 86, 88. The omitted phase windings are disposed aroundthe stationary poles such that the poles 86 on one side of the plungerare north "N" poles while the poles 88 on the other side of the plungerare south "S" poles. The phase A and phase B windings are alternatelydisposed on adjacent stationary poles and adjacent stationary poles aredisposed one pole width apart. The plunger includes a wide pole pair 92and a narrow pole pair 94 disposed on opposite sides of a longitudinalaxis of the plunger. The narrow poles are the same width as a stationarypole while the wide poles are twice as wide as a stationary pole.Starting from the position shown in FIG. 12, the plunger is urgedleftward 96 by the selective energization of the phase A and phase Bwindings. Specifically, as with the embodiment illustrated in FIGS.5(a)-5(f), the energization and deenergization of the phase A and phaseB windings is coordinated such that the plunger is urged leftward tominimize the reluctance path between the poles associated with theenergized phase windings and the poles of the plunger. When the plungerhas reached the left most position, it is maintained there at bycontinuous energization of the phase A windings. A compressible spring98 disposed between the narrow poles 94 and a left-most stop 100, suchas an end of a housing or support that holds the plunger and stationarypoles relative to each other, provides for the return of the plungerrightward when the phase windings are deenergized.

Alternatively, the stationary poles are disposable on one side of theactuator with the phase A and phase B windings disposed on alternatingpoles and forming north-south pole pairs, and the actuator poles aredisposed on a side of the actuator. The actuator is disposed relative tothe stationary poles such that the actuator poles and stationary polesare movable in spaced relation to each other. Moreover, while the springin the above example is disposed for compression, it is to beappreciated that the spring could also be disposed between the widepoles and a right-most stop 102 for extension therebetween duringoperation. The extended spring providing for the return of the plungerrightward when the phase windings are deenergized.

With reference to FIGS. 13(a)-13(e), an alternate embodiment of theinvention is illustrated wherein the stationary element 110, i.e., thestator, includes the novel pole arrangement and wherein the movingelement 112, i.e., the rotor, has uniformly displaced poles. It is to beunderstood that in FIGS. 13(a)-13(e), as with the embodiment of FIGS.5(a)-5(f), the phase windings, the phase drivers, the controller/powersupply, the position sensor and the optional speed control areassociated therewith but have been omitted to facilitate an unclutteredview thereof. To facilitate an understanding of when the omitted phasewindings are energized, the poles associated with an excited phase aremarked with either an `N` or an `S` to signify a north or south polerespectively. The pole arrangement of FIGS. 13(a)-13(e) is configuredsuch that the rotor 112 progresses in a CW direction in response to theselective energization of the phase windings. From the zero degree rotorposition of FIG. 13(a), the phase B windings are energized and the phaseA windings are deenergized. This excitation produces a CW torque on therotor causing alignment of the rotor poles 114(a) and 114(c) withexcited phase B stator poles 116(d) and 116(h), i.e., the rotor polesmove into minimum reluctance position with respect to the energizedphase B poles--the minimum reluctance position corresponding to themaximum inductance of the energized phase windings producing saidalignment. In FIG. 13(b), at 22.5 degrees CW rotor position, the rotorpoles 114(a) and 114(c) and the wide phase B stator poles 116(d) and116(h) have moved to a lower reluctance position with respect to eachother. The reluctance path between the stator poles of the energizedphase B windings and the rotor poles, however, continues decreasing asthe rotor poles continue moving into alignment with the energized phaseB stator poles. Specifically, the rotor experiences a torque due to theinteraction of rotor poles 114(b) and 114(d) with the narrow phase Bstator poles 116(b) and 116(f). Moreover, in the absence of rotor poles114(a) and 114(c) being in a minimum reluctance position with respect towide phase B stator poles 116(d) and 116(h), the rotor also experiencesa torque therefrom. In this manner, in the presence of energized phase Bwindings, torque imparted to the rotor shifts from the wide phase Bstator poles to the narrow phase B stator poles. In FIG. 13(c), at 45degrees CW rotor position, the rotor poles are in minimum reluctanceposition with respect to the phase B stator poles and therefore, notorque is imparted to the rotor from the energization of the phase Bwindings. Energizing the phase A windings, however, causes flux to flowfrom wide phase A stator poles 116(a) and 116(e) through rotor poles114(b) and 114(d). In response to flux flowing therethrough, the rotorexperiences a CW torque causing rotor poles 114(b) and 114(d) to alignwith the wide stator poles 116(a) and 116(e). It is to be appreciated,that as the rotor moves past 45 degrees CW rotor position the phase Bwindings experience an increase in reluctance between the stator polesof the phase B windings and the rotor poles. To avoid having the rotorexperience a CCW torque from energization of the phase B windings incooperation with the increasing reluctance thereof, the phase B windingsare deenergized. In this manner, the torque experienced by the rotorshifts from the phase B windings to the phase A windings. In FIG. 13(d),at 67.5 degrees CW rotor rotation, the rotor poles 114(b) and 114(d) andwide phase A stator poles 116(a) and 116(e) have moved to a lowerreluctance position with respect to each other. The reluctance pathbetween the stator poles of the energized phase A windings and the rotorpoles, however, continues decreasing as the rotor poles move intofurther alignment with the energized phase A stator poles. Specifically,the rotor experiences a torque due to the interaction of rotor poles114(a) and 114(c) with the narrow phase A stator poles 116(c) and116(g). Moreover, in the absence of rotor poles 114(b) and 114(d) beingin a minimum reluctance position with respect to the phase A statorpoles 116(a) and 116(e), the rotor also experiences a torque therefrom.In this manner, in the presence of the energized phase A windings,torque imparted to the rotor shifts from the wide phase A stator polesto the narrow phase A stator poles. In FIG. 13(e), at 90 degrees CWrotor rotation, the phase A stator poles are in minimum reluctancealignment with the rotor poles and therefore, the rotor experiences notorque from the interaction of the wide rotor poles with the phase Awindings. At this position, however, it is to be appreciated that therotor poles and stator poles are in a position similar to the 0 degreeCW rotor position of FIG. 13(a). Accordingly, the description set forthabove for FIGS. 13(a)-13(d) is applicable hereinafter for advancing therotor beyond 90 degrees CW rotor position.

In certain applications, such as aircraft, it is desirable to have amotor also operate as a generator. Specifically, the motor is initiallyused to start, for example, an internal combustion engine, however, oncerunning, the engine drives the rotor such that the motor is useable as agenerator. The present invention is suitable for such applications. Withreference to FIG. 14, a sectional view of a motor-generator (M-G) 10 inaccordance with the present invention with associated control andoperational circuitry connected thereto is illustrated The M-G includesseries wound phase A windings and phase B windings connected to switches45 and phase 46 respectively. The phase A switch selectively connectsthe phase A windings to phase A driver 30 or energy storage means 47.Similarly, phase B switch selectively connects the phase B windings tophase B driver 32 or energy storage means 47. Controller 38 is connectedto the phase switches and the phase drivers for controlling theoperation thereof. The energy storage means stores electrical energyproduced by the generator operation of the M-G in a manner known in theart. When operated as a motor, the controller 38 causes phase A switch45 and phase B switch 46 to connect their respective phase drivers tothe phase windings. The motor is then operated in the manner set forthabove in conjunction with the embodiment of FIGS. 5(a)-5(f) to rotatethe rotor 20 CCW. When used as a generator, however, the controller 38causes the phase A switch and phase B switch to alternately switchbetween their respective phase drivers and the energy storage means incoordination with the position of the rotor relative to the stator.Specifically, by way of example and not of limitation, when used as agenerator, the rotor 20 is driven by an external source such as aninternal combustion engine. With the poles of the rotor in a minimumreluctance position with respect to the poles of the phase A windings,as illustrated in FIG. 14, the controller 38 causes the phase A phasedriver to introduce a first current into the phase A windings therebyinducing a magnetic field therein. Next, the controller causes the phaseA switch to connect the phase A windings to the energy storage means.The external source driving the rotor and stator poles out-of minimumreluctance position, in conjunction with the magnetic field of the phaseA windings, induces in the phase A windings a second current that actsto maintain the magnetic field. This second current charges the energystorage means 47 which in turn provides electrical energy to a load 48,such as lights, aircraft electronics and the like. As the rotor polesare driven into alignment with the phase B stator poles the controllercoordinates the operation of the phase B phase driver and the phase Bswitch as a function of rotor positions such that the phase B windingscharge the electrical storage means in the same manner as the abovedescribed phase A windings.

It is believed that driving the rotor of FIG. 14 CW, versus CCW,produces a change in reluctance between the poles of the rotor andstator that occurs over greater angular position of the rotor relativeto the stator than in the above described generator embodiment or theprior art. It is believed that this change in reluctance over greaterangular position advantageously provides current waveforms having moreuniform amplitude, longer durations with less time between currentwaveforms wherein no current is produced.

Referring now to FIGS. 15-23, an alternate embodiment of the presentinvention is shown. FIGS. 15-22 illustrate a two phase 8/4 switchedreluctance motor 200 having an inner stator 210 and an outer annularrotor 320 that is operable to rotate about stator 210. Stator 210includes eight (8) outwardly extending stator poles designated212(a)-212(h). Each stator pole includes an outward facing stator poleface designated 216. Stator poles 212(a)-212(h) are equally spaced anddefine like gaps 216 between adjacent stator poles. Phase windings 222,224 are disposed around the stator poles to generate magnetic fieldsthat extend through stator 210. Phase windings 222, 224 are disposed onevery other stator pole, and are wound such that each stator pole isadjacent a stator pole of a different phase. Specifically, phasewindings 222 define phase A poles and phase windings 224 define phase Bstator poles. In the embodiment shown, phase A poles 212(a) and 212(c)are north (N) poles, and phase A poles 212(b) and 212(g) are south (S)poles. Similarly, phase B poles 212(b) and 212(d) are north (N) poles,and phase B poles 212(f) and 212(h) are south (S) poles. Phase windings222, 224 are connected in series to sources of switched current (notshown) in a manner similar to that disclosed in FIG. 2. In this respect,the current flows through the phase windings only in one direction. Asindicated above, the phase windings could be parallel connected or acombination of series-parallel connected to their respective sources ofswitched current. A position sensor (not shown) would also be providedto determine the position of rotor 230 relative to stator 210, as shownin FIG. 2.

In the embodiment shown, rotor 230 is illustrated for clockwise rotationrelative to stator 210. Rotor 230 is comprised of an annular ring formedof a magnetic permeable material having inward projecting rotor polesdesignated 234(a)-234(d). In the embodiment shown, rotor poles 234(a)and 234(c) are wide rotor poles having wide pole faces designated 236.Rotor poles 234(b) and 234(d) are narrow poles having inward facingnarrow rotor pole faces designated 238 in the drawings. Wide rotor poleface 236 is dimensioned to span a stator pole face 214 and the gap 216adjacent such stator pole face 214. Narrow rotor pole face 238 isapproximately equal to stator pole face 214. Stator pole faces 214define an angle relative to central axis X of about 22.5 degrees.Likewise, the distance between the corners of adjacent stator pole faces214 defines an angle 22.5 degrees. In this respect, wide rotor pole face236 defines an angle of about 45 degrees and narrow rotor pole face 238defines an angle relative to axis X of about 22.5 degrees. As in theprevious embodiment, wide rotor pole face 236 is approximately twice thesize of a stator pole face 214, and narrow rotor pole face 238 isapproximately equal to a stator pole face 214.

Referring now to the operation of motor 200, rotor 230 moves in aclockwise direction relative to stator 210, in response to thegeneration of north/south pole pairs by the excitation of associatedphase windings 222, 224. FIGS. 15-18 illustrate the progression of rotor230 relative to stator 210 during each phase energization.

Thus, as in the inner rotor/outer stator embodiment previouslydiscussed, motor 200 operates by rotor 230 experiencing a first angularrotation caused by torque generated by the interaction of wide rotorpoles 234(a) and 234(c) with a first pair of energized stator poles, andthen experiences a second angular rotation caused by torque generated bynarrow rotor poles 234(b) and 234(d) interacting with a second pair ofenergized stator poles. Magnetic flux plots corresponding to theposition of rotor 230 and phase energizations of FIGS. 15-18 areillustrated in FIGS. 20-23.

The magnetic flux plots shown in FIGS. 20-23, and those shown in FIGS.6A-6F, illustrate how a motor according to the present inventionoperates between two magnetic states. In the first magnetic state, thewide rotor poles 234(a) and 234(c) are magnetically coupled to statorpoles 212(b) and 212(f). This first magnetic state causes a firstangular rotation of the rotor to bring the leading portion of the widerotor poles into alignment with a set of energized stator poles. As thisoccurs, the motor moves into a second magnetic state wherein narrowrotor poles 234(b) and 234(d) are magnetically coupled to a second setof stator poles 212(d) and 212(h), as shown in FIGS. 21 and 22.

In the first magnetic state, only the wide rotor poles (i.e., only halfof the total number of poles on the rotor) are magnetically coupled tostator poles. In the second magnetic state, the wide rotor poles and thenarrow rotor poles (i.e., all of the rotor poles) are magneticallycoupled to stator poles. Thus, as phases A and B alternate, the motoroscillates between the aforementioned two magnetic states and oscillatesbetween a first magnetic flux circuit configuration (through only thewide rotor poles) and a second magnetic flux circuit configuration(through both the wide and narrow rotor poles). Stated another way, inthe 4/8 motor embodiments shown in FIGS. 6A-6F and FIGS. 20-23, in themotor's first magnetic state, a 2-pole radial magnetic force patternexists in that only the wide rotor poles are magnetically coupled tostator poles and the magnetic flux lines extend primarily through thetwo wide rotor poles and their associated stator poles. In the motor'ssecond magnetic state, a 4-pole radial magnetic force pattern exists asboth the two wide rotor poles and the two narrow rotor poles aremagnetically coupled to stator poles and the magnetic flux lines extendradially through the wide and narrow rotor poles and their associatedstator poles. Thus, in the 4/8 motor shown, the radial magnetic forcepattern changes from a 2-pole pattern to a 4-pole pattern. As will benoted, the number of radial magnetic force patterns is based upon thenumber of wide rotor poles on the rotor. In this respect, a rotor with Xnumber of wide rotor poles would change from a X number pole pattern toa 2X pole pattern.

Importantly, in addition to providing the advantageous operatingcharacteristics previously described, a motor in accordance with thepresent invention provides much quieter operation due to the moreuniform distribution of stresses on the stator. In this respect, twophase motors known heretofore are noisy due to the fact the rotor andstator are magnetically coupled typically at locations 180° apart. Thistype of magnetically coupling distorts the stator by drawing the opposedmagnetically coupled regions of the stators toward each other. In otherwords, the stator is drawn into a non-circular, i.e., an obroundconfiguration. Upon a phase change when the magnetic attractiondisappears, the portions of the stator that are drawn together, snapout, causing vibration and noise in the motor.

The present invention, on the other hand, substantially reducesdistortion of the stator by distributing the stresses more uniformlyaround the stator. This balancing of forces on the stator reduces thedistortion thereof, as well as noise the stator produces duringoperation.

The above embodiments have been described with respect to two phase SRmotors and generators, however, it is to be appreciated by one skilledin the art that the invention described herein is applicable to SRmotor/generators having 3 or more phases, to motors having differingnumbers of stator poles and rotor poles as well as to linear motors.Lastly, in the above described embodiments the stationary element hasbeen referred to as the stator and the rotating or moving element hasbeen referred to as the rotor. It is to be appreciated, however, thatthe choice of this convention is not to be construed as limiting theinvention and in application the rotor or moving element of the abovedescribed embodiment could be stationary while the stator of the abovedescribed embodiment could be the rotating or moving element.

While the invention has been described with reference to the preferredembodiments, obvious modifications and alterations will occur to othersupon reading and understanding the preceding specification. It isintended that the invention be construed as including all suchalterations and modifications to the full extent they come within thescope of the following claims or the equivalents thereof.

Having described the preferred embodiment the invention is now claimedto be:
 1. A switched reluctance motor, comprising:a stator having aplurality of evenly spaced, radially oriented stator poles disposedthereon; a rotor mounted for rotation about a longitudinal axis relativeto the poles of the stator, said rotor having a plurality of radiallyoriented rotor poles disposed thereon, a first rotor pole having a firstrotor pole face of a first size and a second rotor pole having a secondrotor pole face of a second size, different than said first size, saidfirst pole being spaced from said second pole in a direction of rotationof said rotor; and windings for two phases wound about said poles ofsaid stator such that each of said stator poles of one phase isseparated by a winding and an associated stator pole of an oppositephase, said rotor disposed relative to said stator wherein energizationof one of said two phases causes said rotor to be movable apredetermined distance in spaced relation relative to said stator, saidfirst pole of said rotor being in a minimum reluctance relation with afirst energized stator pole when said rotor has moved a first portion ofsaid predetermined distance, and said second pole of said rotor being insaid minimum reluctance relation with a second energized stator polewhen said rotor has moved another portion of said predetermineddistance, said first pole of said rotor remaining in said minimumreluctance relation with said first energized stator pole when saidsecond pole of said rotor is in said minimum reluctance relationshipwith said second energized stator pole.
 2. A motor as defined in claim1, wherein an angle between a pole of the rotor and an adjacent rotorpole in a first direction is a first angle, and an angle between saidrotor pole and said adjacent rotor pole in a second direction is asecond angle.
 3. A switched reluctance motor driven by at leasttwo-phase source, comprising:a stator having an even number "n" ofmagnetically permeable stator poles evenly spaced circumferentiallyabout a central axis, each of said stator poles being radially orientedrelative to said axis and having a stator pole face traversing a firststator angle; a rotor mounted for rotation relative to said stator aboutsaid axis, said rotor having an even number of magnetically permeablepoles spaced about said axis, the number of said rotor poles being ahalf of said number "n," said rotor poles including at least one narrowpole having a narrow face that traverses a first rotor angle, said firstrotor angle being approximately equal to said first stator angle, and atleast one wide pole having a wide face that traverses a second rotorangle approximately twice said first rotor angle, said rotor poles beingdistributed on said rotor, wherein said narrow rotor pole and said widerotor pole move along a same circumferential path, and each of saidnarrow pole faces is spaced from a first adjacent one of said wide polefaces on one side by a first angle equal to about twice said firststator angle and from a second adjacent one of said wide pole faces onanother side by a second angle equal to about three times said firststator angle.
 4. A motor as defined in claim 3, further including aplurality of windings associated with the poles of the stator forconnection to a polyphase source such that energization of a phase ofthe polyphase source forms at least one pair of magnetic poles on thestator that imparts a torque to the poles of the rotor, wherein anenergization of the phase imparts onto the rotor a torque that appearssubstantially on the wide pole face for a first part of said phaseenergization and appears substantially on the narrow pole for a secondpart of said phase energization.
 5. A switched reluctance motor drivenby a two-phase source, comprising:a stator having a plurality of evenlyspaced like poles defining a uniform gap between adjacent of said statorpoles; windings for two phases wound about each of said stator polesthat are circumferentially separated by a respective one of saidwindings and an associated one of said stator poles of a differentphase; and a rotor mounted for rotation about an axis, said rotor havinga radially oriented wide rotor pole and a radially oriented narrow rotorpole, said rotor poles being distributed on said rotor angularly spacedapart about said axis, said rotor poles being dimensioned such that whena first half of said wide rotor pole is in alignment with a first statorpole, said narrow rotor pole is aligned with a gap adjacent a secondstator pole, and when a second half of said wide rotor pole is inalignment with said first stator pole, said narrow rotor pole is alignedwith said second stator pole.
 6. A motor as defined in claim 5, whereinsaid second half of said wide rotor pole is in alignment with a gapadjacent said first stator pole when said narrow rotor pole is alignedwith said second stator pole.
 7. A motor as defined in claim 5, whereinsaid first stator pole and said second stator pole have windings of oneof said two phases.
 8. A switched reluctance motor, comprised of:aninner stator having a plurality of evenly spaced, radially oriented,like stator poles distributed defining a gap between each of said statorpoles, said stator having an "n" number of stator poles wherein "n" is amultiple of four and each of said stator poles having a stator pole faceof a length wherein the length of said stator pole face in a directionof rotation is approximately equal to the gap defined between each ofsaid stator poles; a rotor element mounted for rotation relative to saidstator, said rotor element having a plurality of rotor poles, the numberof said rotor poles being a half said number "n", and one half of saidrotor poles being wide rotor poles and another half of said rotor polesbeing narrow rotor poles, said rotor poles being distributed on saidrotor wherein said narrow rotor poles and said wide rotor poles travelin a same circumferential path, said rotor element dimensioned such thatsaid narrow rotor poles have pole faces approximately equal to the polefaces of said stator poles and said wide rotor pole has a pole facegreater than the pole face of a stator pole; and windings for two phaseswound about stator poles that are circumferentially separated by atleast one winding and an associated stator pole of a different phase,said winding creating a pair of adjacent energized stator poles havingthe same polarity.
 9. A switched reluctance motor driven by a two-phasesource, comprising:a stator having a plurality of like poles, eachhaving a stator pole face, said poles being uniformly spaced to define auniform gap between adjacent poles; windings for each of two phases ofsaid motor wound about stator poles that are circumferentially separatedby at least one winding and an associated stator pole of a differentphase; and a rotor mounted for rotation relative to said stator, saidrotor having a wide rotor pole having a wide rotor pole face, and anarrow rotor pole having a narrow rotor pole face, said rotordimensioned such that said narrow pole face is approximately equal tosaid stator pole face and said wide rotor pole face spans at least thepole face of a first stator pole and the gap adjacent said first statorwhen said narrow pole face is aligned with the pole face of a secondstator pole.
 10. A switched reluctance motor, comprised of:a statorhaving an even number "n" of evenly spaced, like stator poles defining agap between each of said stator poles, each of said stator poles havinga stator pole face and the "n" number of stator poles being a wholemultiple of four; a rotor having a plurality of rotor poles mounted forrotation relative to said stator, a number of said rotor poles beingone-half the "n" number of stator poles, one half of said rotor polesbeing wider rotor poles and another half of said rotor poles beingnarrow rotor poles, said rotor poles being distributed on said rotorwherein a narrow rotor pole is disposed on each side of a wide rotorpole in each direction of rotation, said rotor dimensioned such thateach of said narrow rotor poles has a pole face approximately equal tosaid stator pole face and each of said wide rotor poles has a pole faceapproximately equal to said stator pole face and the gap betweenadjacent said stator pole; and windings for two phases wound aboutstator poles that are circumferentially separated by at least onewinding and an associated one of said stator poles of a different phase,said motor creating one fourth of said number "n" stator and rotor poleinteractions that change to a half of said number "n" stator and rotorpole interactions during each phase energization.
 11. A switchedreluctance motor driven by a two-phase source, comprising:a statorhaving a plurality of like poles evenly distributed thereon, each ofsaid stator poles having a stator pole face; windings for two phaseswound about each of said stator poles that are circumferentiallyseparated by at least one winding and an associated one of said statorpoles of a different phase; and a rotor element mounted for rotationrelative to said stator, said rotor element having a wide rotor polehaving a wide rotor pole face and a narrow rotor pole having a narrowrotor pole face, said rotor poles distributed on said rotor wherein saidnarrow rotor pole and said wide rotor pole travel along a samecircumferential path, said rotor poles being dimensioned relative tosaid stator poles such that said motor has an inductance-to-angularrotation profile wherein the inductance of a phase increases over afirst angle of rotation and decreases over a second angle of rotationand said first angle of rotation is approximately twice said secondangle of rotation.
 12. A switched reluctance motor driven by a two-phasesource, comprising:a stator having a plurality of evenly spaced, likestator poles defining a uniform gap between adjacent said stator poles;windings for two phases wound about each of said stator poles that arecircumferentially separated by a respective one of said windings and anassociated one of said stator poles of a different phase; and a rotormounted for rotation relative to said stator, said rotor having a widerotor pole and a narrow rotor pole disposed wherein said wide rotor poleand said narrow rotor pole travel along a same circumferential path,said rotor dimensioned such that an energization of a phase causes saidwide rotor pole to interact with a first stator pole to induce a firsttorque on said rotor and to produce a first predetermined angularrotation of said rotor, and thereafter causes said narrow pole tointeract with a second stator pole to induce a second torque on saidrotor and to produce a second predetermined angular rotation on saidrotor.
 13. A motor as defined in claim 12, wherein said first statorpole and said wide rotor pole do not produce an opposing torque whensaid first narrow pole interacts with said second stator pole to producesaid second predetermined rotation.
 14. A motor as defined in claim 12,wherein said first predetermined angular rotation of said motor occurswhen said wide rotor pole moves into a minimum reluctance position withsaid first stator pole, and said second predetermined angular rotationoccurs when said narrow rotor pole moves into said minimum reluctanceposition with said second stator pole.
 15. A switched reluctance motordriven by a two-phase source, comprising:a stator having a plurality ofevenly distributed, radially oriented, like poles thereon, each of saidstator poles having a stator pole face; windings for two phases woundabout stator poles that are circumferentially separated by at least onewinding and an associated stator pole of a different phase; and a rotormounted for rotation relative to said stator, said rotor having a widerotor pole having a wide rotor pole face and a narrow rotor pole havinga narrow rotor pole face, said rotor poles being distributed on saidrotor wherein said narrow rotor pole and said wide rotor pole travelalong a same circumferential path, said rotor poles being dimensionedsuch that an energization of one of said two phases causes apredetermined angular rotation of said rotor wherein a first portion ofsaid angular rotation is created by said wide rotor pole being drawninto a minimum reluctance position relative to an energized one of saidstator poles and another portion of said angular rotation is created bysaid narrow rotor pole being drawn into a minimum reluctance positionwith another energized one of said stator poles, said wide rotor polebeing in said minimum reluctance position with said energized one ofsaid stator poles when said narrow rotor pole is in said minimumreluctance position with said another energized one of said statorpoles.
 16. A motor as defined in claim 15, wherein an overlapping ofsaid rotor poles and said stator poles occurs during rotation of saidrotor, and the overlapping of said rotor poles and said stator polesincreases generally uniformly during said predetermined angular rotationof said rotor.
 17. A motor as defined in claim 16, wherein a width of anarrow rotor pole face is approximately equal to a width of a statorpole face and a width of a wide rotor pole face is approximately equalto twice said width of a stator pole face.
 18. A motor as defined inclaim 17, wherein said narrow rotor pole face is slightly larger thansaid stator pole face and said wide rotor pole face is slightly largerthan twice the width of said stator pole face.
 19. A switched reluctancemotor driven by a two-phase source, comprising:a stator having aplurality of like poles evenly distributed thereon to define a uniformgap between each pole, each of said stator poles having a stator poleface; windings for two phases wound about said stator poles that arecircumferentially separated by at least one winding and an associatedone of said stator poles of a different phase; and a rotor elementmounted for rotation relative to said stator, said rotor element havinga wide rotor pole having a wide rotor pole face and a narrow rotor polehaving a narrow rotor pole face, said rotor poles distributed on saidrotor element wherein said narrow rotor pole and said wide rotor poletravel along a same circumferential path, said rotor poles beingdimensioned such that a uniform gap is defined between said rotor polefaces and said stator pole faces and wherein an energization of one ofsaid two phases causes said wide rotor pole to magnetically interactwith a first stator pole and said narrow rotor pole to magneticallyinteract with a second stator pole to cause said rotor element to rotatea predetermined angular amount, and an area of overlap of said rotorpole faces relative to said stator pole faces to increase at a generallyuniform rate as said rotor element moves said predetermined angularamount.
 20. A motor as defined in claim 19, wherein said motor has aninductance profile related to an angular rotation for each phase whereinsaid inductance profile increases over a first angle of rotation anddecreases over a second angle of rotation, and said first angle ofrotation is substantially greater than said second angle.
 21. A motor asdefined in claim 20, wherein said first angle of rotation isapproximately twice said second angle of rotation.
 22. A switchedreluctance motor driven by a two-phase source, comprising:a statorhaving a 2X number of evenly spaced, radially oriented, like polesdefining a gap between adjacent stator poles; windings for two phaseswound about said stator poles wherein said stator poles arecircumferentially separated by one of said windings and an associatedone of said stator poles of a different phase; and a rotor mounted forrotation relative to said stator, said rotor having an X number of rotorpoles and at least one wide rotor pole and at least one narrow rotorpole, said rotor dimensioned such that, during each phase energizationsaid motor has a first state wherein a 1/2X number of said rotor polesare magnetically coupled to a like number of stator poles and a secondstate wherein said X number of said rotor poles are magnetically coupledto a like number of stator poles.
 23. Motor as defined in claim 22,wherein in said first state said at least one wide rotor pole ismagnetically coupled to a first stator pole, and in said second statesaid at least one wide rotor pole is magnetically coupled to said firststator pole and said at least one narrow rotor pole is magneticallycoupled to a second stator pole.
 24. A motor as defined in claim 23,wherein each of said stator poles has a stator pole face width of afixed dimension, said at least one narrow rotor has a pole face widthapproximately equal to said stator pole face width and said at least onewide rotor has a pole face width approximately equal to twice saidstator pole face width.
 25. A switched reluctance motor driven by atwo-phase source, comprising:a stator having a yoke and an even number Nof evenly-spaced, like stator poles distributed on said yoke defining agap between each said stator poles; windings for two phases wound aboutstator poles that are circumferentially separated by a respective one ofsaid windings and an associated one of said stator poles of a differentphase; and a rotor mounted for rotation relative to said stator, saidrotor having a half of said even number N of rotor poles, said rotorhaving at least one wide rotor pole and at least one narrow rotor pole,and said rotor poles being dimensioned such that when said windings fortwo phases are alternately energized, said rotor poles interact withsaid stator poles such that said motor operates between a first statewherein half of said rotor poles are magnetically coupled to a likenumber of said stator poles and a second state wherein all of said rotorpoles are magnetically coupled to a like number of stator poles.
 26. Amotor as defined in claim 25, wherein in said first state, said at leastone wide rotor pole is magnetically coupled to a first stator pole, andin said second state, said at least one wide rotor pole is magneticallycopied to said first stator pole and said at least one narrow rotor poleis magnetically coupled to a second stator pole.
 27. A motor as definedin claim 26, wherein each of said stator poles has a pole face width oflike dimension, said at least one narrow rotor pole face has a widthapproximately equal to a stator pole face width and said at least onewide rotor has a pole face width approximately equal to twice a statorpole face width.
 28. A motor as defined in claim 25, wherein said motorchanges from said first state to said second during said each phaseenergization.